In many applications, it is desirable to use as a feed stream air or other gaseous mixture that is substantially free of any entrained liquids as aerosols and particulate matter, the presence of these impurities often substantially affecting the efficiency of a device using this feed stream. By way of example, consider an oxygen concentrator, one of the principle elements in an oxygen generation system used aboard some aircraft. If the air entering this concentrator is contaminated by liquid aerosols, concentrator efficiency may be lowered by as much as thirty percent. Liquid aerosols are also suspected of causing the molecular sieve used in oxygen generation beds to disintegrate, resulting in early system failure.
In view of the problems which may be encountered when liquid aerosols are present, it has become common practice to attempt to remove liquid aerosols by first employing the use of a separator, this device having the ability to remove the bulk of liquid aerosols entrained in the entering air or gas stream. The finer aerosols, which follow the streamlines of the gas and are not removed efficiently by this means, are conducted to a coalescing medium. The coalescer is typically located a varying distance downstream from the separator. On contact with the coalescer, the fine aerosols form droplets on the medium. To the extent any of these droplets become large enough to be influenced by gravitational forces, such droplets fall into a sump which may be drained as required.
It is also common in aircraft systems to have an ultra-fine filter medium, such as a HEPA-rated filter for particulate removal located downstream from the coalescing medium. These types of filters will also fail or operate at a reduced level of efficiency if contaminated by liquid aerosols. To preclude possible contamination, there is a minimum recommended spacial separation to be used between the coalescer and HEPA-rated filter. Alternatively, others have placed two HEPA-rated filters in series and spaced so as to prevent liquid carryover by the airstream.
Moreover, the previously described problems associated with the presence of liquid aerosols can become exacerbated if the gas being conducted from the separator to the coalescing medium encounters an environment which cools the gas to its dew point. This cooling can result not only in the formation of additional aerosols, but can also result in liquid aerosols passing through the coalescing medium while still in the liquid phase, an effect which is undesirable in certain applications, such as the aircraft environment described previously.
Compounding the problems evident in the approaches and systems described above, space and weight efficiency are of considerable importance in aircraft applications.